DKIM means DomainKeys Identified Mail
DKIM is a technique in which an organization can take responsibility for a message sent by e-mail. In fact, DKIM originated from 2 separate techniques: DomainKeys of Yahoo! and Internet Identified Mail from Cisco. DKIM is a base for authentication and not anti-spam technology, but it is often used to prevent spam. By checking the authenticity of a mail server, spam can be fought. With DKIM block you no fake email, you only mark a message as invalid. What will be done next is the handling of the e-mail. Https://www.youtube.com/watch?v=yHv1OPcc-gw